Chrysotile long fibers have been, as descrived in the previous report, synthesized with the addition of magnesium bromide to a raw material mixture of chrysotile composition by dehydration reaction from slurry of the raw material mixture. In the present experiment, pressure variation on the reaction period was measured to be determined the initial and final pressure for obtaining the best yield of the fibers. Based on considerations from the decreasing of partial pressure of water, it was deduced that fibers were formed in such a concentrated slurry that in the final state a near to gel state was attained. An addition of ferrous ions to the slurry exerted a negative effect on the formation of the fibers; a small amount of addition resulted in decreasing in yield, and no fibers were formed in the case of a large amount.
When ferric hydroxide gel as the trivalent ions was added to the slurry, the temperature of formation of fibers was lowered proportionally with the iron content and the degree of this lowering was in accordance with the values calculated from Vegard's low based on Bowen's results. In this case, the trivalent iron was reduced to drivalent by hydrogen evaporated by the dehydration process. This reduced iron might be selectively combined with silica. In the case of the best yield, moreover, the temperature of the formation became lower than the limit of the formation. This temperature drop was seemed to have resulted from the enrichment of the iron at the boundary between the forming fibers and the reacting bulk.

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This research was carried on as a part of the study on the synthesis of topaz [Al₂SiO₄F_x(OH)_2-x]. Mixtures of SiO₂ and Al₂O₃ gels and AlF₃ specimens corresponding to compositions Al₂SiO₄F_x(OH)_2-x, where x=0.0, 1.0, 1.5 and 2.0 were treated at temperature ranging from 300° to 2200°C at pressures ranging from the atmospheric pressure to 70kb using squeezer and girdle type high pressure apparatus. The heat treatment temperature was measured by a platinum-rhodium thermocouple inserted in the specimen chamber or was estimated from the relations between the temperature and heating power imput at several pressures. Minerals in the treated specimens were identified by the X-ray diffraction method, the infrared spectroscopy and the microscopic observations.
No topaz was found in the heat-pressure treated products of the mixture of x=0.0. Under 700°C, pyrophyllite, corundum, and α-quartz etc. were formed as the crystalline phases at arbitary pressure. Kyanite was stable at pressure over about 30kb at 1000°C and above 35kb at 1500°C. Under these conditions, sillimanite, mullite and silica were obtained. Above 1900°C at 40kb, liquid and vapor phases were found.
In the specimen of x=1.0, topaz was stable at pressures above 10kb at 1000°C and above 30kb at 1600°C. Under these pressures at the respective temperatures, mixture of mullite and silica was obtained as the stable crystalline phases. It seems that topaz melts incongruently to corundum, liquid and vapor at temperatures from 1700°C to 1900°C at 40kb. Liquid and vapor phases were found above 1900°C at same pressure.
In the specimen of x=2.0, it was obtained nearly similar result in comparison with a case of x=1.0, but a stability region of topaz was expanded wider.
Maximum size observed of synthesized topaz was about 0.2mm long. The color of topaz was slightly transparent.

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純粋なMgO単結晶中と, 添加物を加えたMgO単結晶中のNi²⁺の拡散係数を求めた. Cr₂O₃とFe₂O₃を添加した時, Ni²⁺の拡散は促進された. CoO添加の時には, そのような効果がなかった. Cr₂O₃ Fe₂O₃添加の時にはFe³⁺, Cr³⁺がMg²⁺と置換するために, 原子価の違いにより陽イオン空孔が生じ, それがためにNi²⁺の拡散が促進されるものと思われる. CoO添加では陽イオン空孔は生じない. 純粋な (無添加) MgO単結晶中と, 添加物を加えた場合の拡散の活性化エネルギーの比較により, 無添加の場合にも不純物による欠陥が大きな役割を成しているものと思われる.

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SiC crystals grown in the cavity of a Lely furnace have been studied experimentally at 2500°C. In this study, special attention was called to the initial stage of recrystallization.
The results obtained are summarized as follows;
1) At the initial stage of recrystallization, β-SiC often crystallizes out. These crystals of β-SiC disappear with the progress of the subsequent recrystallization.
2) Two dimensional growth layers having no growth spiral are often observed on the basal surfaces of the initial platelets. Most of these crystals show one-dimensional disorder.
3) The transition from β- to α-SiC at about 2500°C seems to occur mainly through a vapour phase.
4) When the growth cavity is poorly supersaturated, β-SiC fails to appear. In this case, however, α-SiC initially formed often shows one dimensional disorder.
5) From these experimental results, it is concluded that the thermal stability gap between SiC polytypes has a certain relation to the kind of polytype to occur.

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